The intensive care of a great many patients with respiratory difficulties involves the use of a translaryngeal endotracheal tube for prolonged periods, unless a tracheostomy is performed. In neonates and young children the latter is a last resort, but long term intubation carries considerable risk of damage to trachea and larynx, particularly from the inflatable cuff. Recent studies on laryngeal mechanisms indicate that an important etiological factor in the complications is the mismatch between tubes presently in use and the conformation and movements of the air passages. This project proposes to measure the relevant forces in the larynx and tube, using a primate model, by means of appropriately instrumented catheters, in order to determine the extent of the mismatch and the required properties of a redesigned tube. The data so obtained will guide the manufacture in the Bioengineering Workshop of the University of Washington of biomechanically correct tubes, embodying at least two new design features derived from laryngeal biomechanical considerations. The new tubes, it is expected, will be able to dispense with a cuff. They will be tested in primates of different sizes, modeling the newborn, young children, and adolescents. The effects and aftereffects on the walls of the air passages will be evaluated and compared by means of fiberoptic photography and cinematography, and histological examination, including light microscopy and scanning electron microscopy of the epithelial surface. The results should provide a reliable estimate of the serviceability of the new tubes in critically ill patients, particularly infants.